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A question for physicists

Posted on: June 3, 2007 - 7:25am

Jacob Cordingley

Posts: 1484

Joined: 2007-03-18

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A question for physicists

I've recently been ploughing my way through Carl Sagan's Cosmos on www.tv-links.co.uk. In one episode he mentions the possibility of time travel backwards by going faster than the speed of light. I've always considered time travel backwards to be impossible, but I was also in disbelief when he said that time would actually slow down at the speed of light, i.e. what might seem like days for travellers at the speed of light would actually be years, even millenia on Earth, it goes against my common human intuitions on time. I'm well aware of the weaknesses of the human mind to understand this. I have a great philosophical, ethical and political mind but when it comes to this I don't have a fucking clue.

Time travel is a theoretical possibility by travelling through wormholes, which would be an extremely efficient way of doing it. A rent of such magnitude would undoubtably only be achievable by a Type II civilization on the Kardavesh scale. In theory, travel into the future should be relatively easy, but into the past would be fiendishly difficult.

As for Sagan's suggestion, I am sceptical to the point of saying it is totally impossible. No material entity can travel at anything close to light speed. The Lorentz-Fitzgerald contraction dictates that paramaters start to change at those speeds. For instance, the distance of one meter actually contracts. This does not mean a material body one meter in length contracts (the atoms don't squish) but rather that the space-time itself contracts, this is because there is no constant frame of reference except the speed of light. Another effect is that the closer one goes to light speed, the more mass one gains, which invariably slows one down. Light, having no mass, is not bound by this. But an entity with mass (the force which causes an object in motion to continue) would reach infinite mass at the speed of light. In fact, on the blackboard alone, the absolute maximal speed for a material object to travel at is around 15% of light speed (after that, the mass gained offsets the speed increase). This is called critical mass.

So I think Sagan's suggestion is impossible. Every physicist I have met who has an opinion on time travel believes the only possibility is via wormhole travel.

"Physical reality” isn’t some arbitrary demarcation. It is defined in terms of what we can systematically investigate, directly or not, by means of our senses. It is preposterous to assert that the process of systematic scientific reasoning arbitrarily excludes “non-physical explanations” because the very notion of “non-physical explanation” is contradictory.

deludedgod is correct. Your total mass asymtopes at the speed of light in a vacuum, meaning at that point your mass would be infinite, and the amount of energy needed to accelerate to that point would also be infinite, and spacetime would be infinitley small (in other words, totally collapse)

So traveling at the speed of light is impossible, no less traveling faster than the speed of light. Not even light itself can travel faster than 3.0X10^8 m/s (speed of light).

The only way you could go back in time is to make a wormhole with a built in time dialation. What I mean by this is if you are somehow able to tunnel through spacetime and create a wormhole (with intense gravity or some other force), one end of the wormhole will be at a different point in both space and time. What you could then do is either move the wormhole at very high speeds, or place it next to a black hole. Then, after several years remove the wormhole from this state, go into the other end of the wormhole, and when you came out you would be several years in the past.

The problem with this though, is that you wouldn't be able to go back any further than when the wormhole itself came into existence.

There might even be cases where this has naturally happened. Wormholes might have formed near the beginning of the universe, and there is an off chance that one end of them might be near a black hole or neutron star. If you found such a wormhole (and its other end), you would be able to travel many millions of years into the past (not that you'd want to do that)

Call me a little sceptical. I know that wormholes are supposedly ex black holes in which the mass has gained such a high density that it disappears, leaving behind it's gravity. My question is how would it be possible for us to travel through a wormhole and not be crushed?